Maximum intensity maps (MIM) for Portugal mainland

Abstract

Maximum intensity maps (MIM) may represent, as a first approach, the seismic risk of a certain region. In Portugal, the last MIM dates back to the eighties, suffering minor updates since then, and was based on the intensity distribution (isoseismals) of the major earthquakes affecting Portugal. Using GIS, we draw a more detailed map, not based on the isoseismal curves but based on the individual observations (intensity data points). A revision and compilation of all available macroseismic information was performed resulting on 5544 intensity data points (IDP). A MIM was produced using kriging interpolation in a GIS but inserting also the individual observations. The differences and similarities between this map and the previous one are discussed. To compare with the seismic zoning presented in the Portuguese seismic code, we performed, separately, a MIM considering only the earthquakes occurring on the NEAR seismic source zones and other MIM considering only the FAR seismic source zones. These maps were compared to the Portuguese seismic code zoning. The results obtained and discussed in this study present a high level of detail and could contribute for a better definition and estimation of the seismic hazard and risk in Portugal.